Apparatus for pre-drying matrices



Oct. 25, 1966 L. H. SATRE ETAL 3,280,475

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APPARATUS FOR FEE-DRYING MATRICES Filed April 28, 1960 6 Sheets-$heet 3 INVENTORS.

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APPARATUS FOR FEE-DRYING MATRICES Filed April 28. 1960 6 Sheets-Sheet 5 NVENTORS.

AHA/v0 JATZE' 6 4245? 1. 5020577 AJPF? 4, 5020577 Oct. 25, 1966 L. H. SATRE ETAL APPARATUS FOR FEE-DRYING MATRICES 6 Sheets-Sheet 6 Filed April 28. 1960 I I I I T 5 L w. m Z M M? (M r6 r E a 1 [H im 1 5 A Z M Y B United States Patent 3,280,475 APPARATUS FOR PRE-DRYING MATRICES Leland H. Satre and Charles L. Burdett, Whittier, and Jasper A. Burdett, Norwalk, Calif., assignors, by mesne assignments, to Leland H. Satre, North Plainfield, NJ.

Filed Apr. 28, 1960, Ser. No. 25,400 3 Claims. (Cl. 3453) The invention relates to apparatus for pre-drying matrices to be used in casting stereotype plates for printing presses, particularly the pre-drying of such matrices before final drying and shaping thereof in a forming machine or former.

In the making of stereotype plates for printing presses, the type is first locked up in a chase. A moist mat is then pressed upon the type to transfer an impression of the type to the mat and thus form a matrix. The mat is composed principally of a papier-mache material. The matrix is then pre-dried to remove most of its moisture. The pre-dried matrix is then placed in a forming machine for final drying and for forming of the matrix to the shape of the printing press plate. The dried and formed matrix is used subsequently as a mold for casting the metal stereotype plate to be used on the printing press cylinder for the actual printing. The pre-drying of the matrix removes most of its moisture and is a crucial step which gives rise to several problems.

The problems involved in the pre-drying of a matrix include the following: First, it is desired that the reduction in area of the matrix due to shrinkage caused by the predrying be substantial. This permits of a smaller page area in the printing with a consequent saving of newsprint paper. The saving may be very substantial for large circulations over a period of time. Second, the matrix must be prevented from buckling or rippling during pre-drying. Buckling may result from non-linear shrinkage of the matrix during drying or anomalies in the material of the matrix. It may also result from improper and inadequate support of the matrix during pre-drying. Buckles and the like in the matrix cause corresponding imperfections in the stereotype plate ultimately cast therefrom, which results in defective printing with the plate. Third, it is necessary that there be maximum retention of molded depth of the matrix. The molded depth of the matrix is the depth of those impressions in the matrix made with the type by compaction of the mat, such as the impression made for the body of an e relative to the portion of the matrix which will form the eye of the e. It is to be distinguished from mere deformation of the mat, such as the actual bending of the mat to create large nonprinted areas. If molded depth is not retained in the matrix, the stereotype plate will be defective in that the ink rolls will bottom out on the portions which are intended to appear white, such as the eye of an e, and such areas will not appear white in the printing. Loss of molded depth during pre-drying is caused principally by resilient recovery of the compaction impressions in the matrix.

Conventional machines in the printing industry for predrying matrices do not provide satisfactory solutions to the above problems. Matrices pre-dried with such machines frequently have buckles, inadequate areal shrinkage and/or inadequate retention of molded depth. Buckles are particularly likely when the relatively thin standard mats are used, and inadequate areal shrinkage and inadequate retention of molded depth are particularly likely when the relatively thick packless mats are used.

We have found that the above problems in the predrying of matrices are effectively solved if a side of the moist matrix is lightly held on and urged against a supporting surface having an area at least coextensive with 3,280,475 Patented Oct. 25, 1966 the area of the side of the matrix and, while so held, large substantially equal amounts of heat are rapidly and simultaneously applied substantially uniformly to each side of the matrix. Buckling of the matrix is inhibited by the matrix being urged against the supporting surface and by heating each side of the matrix simultaneously and substantially uniformly and equally. The large amount of heat produces the desired areal shrinkage of the matrix, and since the matrix is only lightly held, such shrinkage is not thereby inhibited. The rapid high heating of the matrix also causes its surface to quickly take an initial set, and this prevents resilient recovery of compaction impressions in the matrix, thus retaining molded depth.

Consequently, our invention in a method for pre-drying matrices includes the steps of supporting substantially heat non-absorptively a side of the matrix, lightly urging the supported side of the matrix against its supporting surface, and then, while the moist matrix is so urged against the supporting surface, applying rapidly and simultaneously large, substantially equal amounts of heat substantially uniformly to each side of the matrix.

The apparatus of our invention to implement the method thereof includes a minimal heat absorptive support means for supporting a side of va moist matrix placed on it, holding means for urging the supported side of the moist matrix against the support means, and heating means adapted to apply simultaneously substantially equal amounts of heat to each side of the moist matrix.

The invention will be more clearly understood by reference to the following detailed description thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an elevational side view, partially broken away, of the apparatus of the invention;

FIG. 2 is an elevational end view of the apparatus looking along line 2-2 in FIG. 1;

FIG. 3 is a sectional view taken along the line 33 in FIG. 1;

FIG. 4 is a sectional view taken along the line 4-4 in FIG. 1;

FIG. 5 is a sectional view taken along the line 5-5 in FIG. 1; and

FIG. 6 is an electrical circuit diagram for the apparatus.

The method of the invention comprises the following steps: First, supporting substantially heat non-absorptively a side of a moist matrix. Such manner of supporting the matrix enables substantially equal heating of each side thereof. In order that the supporting surface is substantially non-absorptive of heat, it is preferably a reticulated surface with maximum open area, on the order of eighty percent open area, uniformly distributed, being satisfactory, and it has minimum mass and minimum volume, is made of metallic material, and is polished, smooth and light in color, so that it is capable of absorbing and conducting only minimal amounts of heat. Preferably, the supporting surface is substantially planar and is a screen tensioned or prestressed in its planar extent in order to make it substantially planar. However, the supporting surface may be slightly curved as explained below. Second, placing a moist matrix on the supporting surface. The moist matrix is so placed for pre-drying in accordance with the method of the invention. Third, lightly urging substantially uniformly the moist matrix against its supporting surface. This urging removes buckles from the moist matrix and holds it in such condition, but since it is only a light urging, areal shrinkage of the martix is not inhibited thereby. Preferably the holding pressure exerted against the side of the matrix opposite the supported side thereof is on the order of onethird pound per square inch. This holding pressure is preferably produced by creating differential gas pressure on the sides of the matrix, with the higher pressure on the side of the matrix opposite the supported side.

Fourth, while the moist matrix is so urged against the supporting surface, rapidly and simultaneously applying substantially equal, large amounts of heat substantially uniformly to each side of the moist matrix. This rapid, equal drying of both sides of the matrix while it is lightly urged against the supporting surface yields the advan tageous results explained above. During the application of the heat, circulation of air or other gas past and around both sides of the matrix is provided to remove vaporized moisture from the region of the matrix. After the heat has been applied for a desired time period, it is turned off, the holding pressure is released, and the pre-dried matrix is removed from the supporting surface.

Apparatus of the invention to implement the method thereof may take the form of the matrix pre-drier shown in FIG. 1, designated generally with the reference numeral The pre-drier It) has a generally parallelepiped outer framework 11, made of angle-iron or the like, which at 12 and 13 supports the pre-drier on a supportive surface. Preferably, the pre-drier has an upper inclined face 14. The framework 11 is exteriorly sheathed on all sides with covering material 15, such as sheet metal.

drying chamber 16 has a generally parallelepiped framework 17, made of angle-iron or the like, which is sheathed on all sides with air impermeable material 18, such as sheet metal. The sheathing 18 on the drying chamber terminates on all sides thereof at 60 and at the support means 19, so that an open space is provided for entrance of air into the drying chamber.

Centrally disposed in the drying chamber 16 is support means 19 adapted to support a moist matrix to be predried. A slot 50 is formed in the face 14 in alignment with the support means 19 and is equipped with laterally adjustable guides 51, 52, so that a moist matrix to be predried may be inserted through the slot to be supported on the support means 19. As best shown in FIG. 3, the support means has a support member or surface 29 which is mounted on a frame 21. The support member 20 is constructed so that it has minimal heat absorption and conduction characteristics. To this end, the support member 20 has minimum mass, minimum volume, maximum open area, and is made of polished, smooth, light-colored material. Preferably the support member 20 takes the form of a reticulated metallic surface or screen. Alternatively, the support member may be a very thin powdered metal membrane extending over the frame 21, or it may be metal honeycomb material. \Vhen the support memher is a screen, the mesh, or number of strands per inch, of the screen and the tensile strength of the strands of the screen are of critical importance. The area of the mesh openings should be as large as possible for maximum open area, and thus for minimum mass and volume, of the screen, but it must not be so large that a moist matrix supported thereon will deform into the openings to assume 'a waffle pattern. It is preferred that the screen be planar,

and to achieve this, it is fastened to the frame 21 with conventional means, such as a metal strip 105 fastened to the frame 21 and sandwiching the screen between the frame 21 and the strip 105, in planarly tensioned condition produced by prestressing of its strands. The greater the tensioning of the screen the better, because there will then be less deflection of the screen from planar configuration when a moist matrix is placed thereon and lightly urged thereagainst. The capacity of the screen for tension depends on the tensile strength of the individual strands of the screen and also on the mesh of the screen. The area of the mesh openings is made as large as possible, as explained above. The strands of the screen are of maximum tensile strength so that they can be maximumly prestressed but have minimal cross-sectional area for minimal heat conduction characteristics and minimal mass and volume of the screen as a whole. It has been found that the above requirements are satisfactorily met when the overall dimensions of the screen are approximately 19 inches by 23 inches, and it is made of .010 inch diameter, bright stainless steel wire Woven with 16 such wires per inch each way, or a 16-mesh screen. Piano wire may be used in place of stainless steel Wire, but it has the disadvantage of being difficult to form into a screen because of its stiffness and consequent resistance to weaving. The 19 by 23 inch dimensions of the screen are adequate to accommodate most matrices, but other dimensions may be utilized. If desired, the support means 19, including the support member 20, may be slightly curved. This curvature may be convex on the matrix side of the support means to compensate for deflection of the support member caused by urging thereagainst of a matrix supported thereon. Or, the support means may be curved either concavely or convexly on the matrix side thereof to cause the matrix to be pre-dried while held in an arcuate configuration. Pre-drying the matrix while it is held in curved configuration may be advantageous either because the resulting curved pre-dried matrix may be more adaptable to forming in a former, or, particularly when certain types of matrices are pre-dried, a more planar predried matrix may result from the balancing of internal stresses in the matrix induced by the curved configuration thereof and by the heating thereof.

Within the drying chamber 16 there are disposed heating means on each side of the support means '19'which are adapted to supply rapidly large, substantially equal amounts of-heat substantially uniformly to each side of a matrix supported on the support means 19. Preferably the heating means are sources of radiant heat energy because radiant heat sources tend to be uncomplicated and inexpensive and well adapted to supply large amounts of heat very rapidly. Alternatively, the heating means may take the form of convection heating with heated gas, but this is not preferred because of the more complex and expensive apparatus which would be necessary and, more importantly, because convection heating is not well adapted to supply large amounts of heat very rapidly. Although the heating means for supplying radiant heat energy may take various forms, it has been found satisfactory to utilize an equal number of infra-red electric heating lamps spaced approximately equally from the sup-port member 20 of the support means 19 on each side thereof at 22 and 23. Preferably, the heating lamps 23 are spaced slightly closer than the heating lamps 22 to the support member 20 to compensate for its absorption and conduction of heat resulting from its interposition between the heating lamps 23 and the matrix to be predried, so that each side of such matrix receives substantially equal amounts of radiant heat energy when the heating means are in operation. When the support member 20 is approximately 19 inches by 23 inches in size, it has been found satisfactory to use twenty ZSO-watt infra-red electric heating lamps for each heating means 22, 23.

Holding means is provided for lightly and substantially uniformly urging a moist matrix supported on the support member 20 against such support member. The urging must be uniformly distributed over the area of the matrix so that it is uniformly urged against the support member. It must be only a light urging so that areal shrinkage of the matrix is not inhibited, excessive deflection of the support member is not produced, and, when the support member 26' is reticulated, deformation of the matrix into the openings of the support member is not present. The holding means is adapted to operate continuously so that the matrix may be so urged during the entire period that it is subjected to heat in the drying chamber. Preferably, the light urging of the matrix against the support member is produced by creating a slightly higher gas pressure on the side of the matrix opposite the side thereof supported on the support member 20. This differential gas pressure may be created by means of an exhaust blower 30 which is adapted to rernove air from the lower portion of the drying chamber, which since all sides of the lower half of the drying chamber, extending from the support means 19 to the heating means 23, are covered with sheathing 18 and the support member 20 is substantially entirely covered with the matrix, creates a sub-atmospheric pressure in such portion of the drying chamben The pressure differential is slight for the reasons explained above, preferably being on the order of one-third pound per square inch. The exhaust blower 30 discharges through the outlet duct 31 thereof. Alternatively to creating a subatmospheric pressure on the side of the matrix adjacent to the support member 20, there may be created a pressure slightly higher than atmospheric on the other side of the matrix in order to create the desired pressure differential acting on the sides of the matrix.

Means are provided to circulate air through the drying chamber 16 and past and around the matrix which is being pre-dried on the support means 19 to remove vaporized moisture from the drying chamber. This means operates continuously during the period the heating and holding means are operative. In order that air may enter the drying chamber, the sheathing 18 thereon terminates at 60 and at the support means 19, as heretofore explained in connection with the construction of the drying chamber. Air which thus enters the drying chamber circulates into the lower portion of the drying chamber past the edges of the matrix being pre-dried on the support means 19, since although the matrix substantially covers the support member 20, it is not entirely coextensive therewith and consequently air passage spaces remain between the periphery of the matrix and the inner periphery of the support means frame 21. Such air entering the lower portion of the drying chamber is, of course, exhausted therefrom by means of the exhaust blower 30. Air entering the upper portion of the drying chamber is exhausted therefrom by means of a second exhaust blower 106 which exhausts through its outlet duct 107. The second exhaust blower 106 is of smaller capacity than the exhaust blower 30 so that, although a slight sub-atmospheric pressure is created within the upper portion of the drying chamber by means of the second exhaust blower 106, nevertheless, the gas pressure in the upper portion of the drying chamber is greater than the gas pressure in the lower portion of the drying chamber, preferably being on the order of one-third pound per square inch greater, as heretofore explained.

The matrix pre-drier is provided with operating means which functions to turn on the heating means, the holding means, and the means for circulating air through the drying chamber when a moist matrix to be predried has been placed on the support member 20, to continue simultaneous operation thereof for a predetermined time period, and to turn them off at the end of the time period and discharge the pro-dried matrix from the apparatus. The operating means includes a start microswitch 61, a timer 62, and release mechanism. As best shown in FIGS. 4 and 5, a transverse aperture 109 is formed in the sheathing 18 across the side of the drying chamber opposite from the slot 50 by reason of the sheathing terminating at 60 and at the support means 19. The aperture 109 is aligned with the lower end of the support means 19 so that a pre-dried matrix may move from the support means through the aperture. Blocking movement of a matrix through the aperture 109 is a stop 35 which extends vertically across the aperture. The stop 35 is operatively connected to the start microswitch 61. The start microswitch 61 is normally open, but when a matrix has been disposed on the support means 19, the inclination of the support means causes the matrix to move against the stop 35 and thus move the stop to actuate the microswitch to a closed position. So long as the matrix bears against the stop 35, the start microswitch 61 is maintained in closed position. The start microswitch 61 functions to simultaneously turn on the heating means, comprised of the electric infra-red heating lamps 22 and 23, to turn on the holding means, comprise-d of the blower 30, to turn on the means for circulating air through the drying chamber, comprised of the second exhaust blower 106, and to actuate timer 62. The timer 62 is set to predetermine the time period during which the heating means and holding means shall simultaneously operate. When the timer 62 has run for the predetermined time period, it functions to momentarily energize a release solenoid 63 and also to turn off the exhaust blowers 30 and 106 and the electric infra-red heating lamps 22 and 23. The release solenoid 63, shown in deenergized condition in FIG. 5, is suitably mounted on the drying chamber by means of brackets 82 and has an armature 64 which is pivotally attached to a release yoke 65 intermediate the ends of the yoke. One end of the release yoke 65 is connected to an extension return spring and the other end is pivotally connected at 67 to one arm of a bell-crank 66. The bell-crank 66 is fixed to a shaft 81. The shaft 81 extends through and is journalled in the outlet duct 31 of the blower 30. Attached to the shaft 81 is a damper blade 83 which rotates with the shaft 81. The momentary energization of the release solenoid 63 pulls down on the release yoke 65 and thus rotates the shaft 81. If necessary, the pivotal connection of the armature 64 to the yoke 65 may be by means of an elongated slot in the yoke to permit longitudinal movement of the yoke when it rotates the bell-crank 66. This rotation of the shaft 81 causes the damper 83 to be revolved into the flow of exhaust air coming from the freewheeling exhaust blower 30 previously turned off by the timer. The air flow impinging against the damper 83 holds it across the outlet duct 31 until the blower has slowed to a point where the force of such air flow impinging against the damper 83 is insufficient to resist the return mechanism. The other arm of the bell-crank 66 is pivotally attached at 71 to an upwardly extending link 68 which at its upper end is pivotally attached at 72 to a release lever 69. The release lever 69 is pivotally carried on the drying chamber by means of a pivot 70 which is mounted on a transversely extending member 84. Adjacent the end of the release lever which is pivotally attached to the link 68 is a second extension return spring 85. The two return springs 80 and constitute the return mechanism to return the release mechanism to its normal position when the force of the exhaust air from the blower 30 impinging against the damper 83 is no longer suificient to resist their force. The start microswitch 61 is mounted on the end of the release lever opposite the end thereof connected to the link 68. Consequently, the momentary energization of the release solenoid 63 and the holding of the mechanism in rel-eased position by means of the damper 83 being turned into the exhaust air flow causes the arm of the bell-crank 66 connected to the link 68 to rotate the release lever 69 about its pivot mounting 70 and consequently lift the stop 35, together with the start microswitch 61, so that the stop 35 clears the matrix on the support means 19. This permits the pre-dried matrix to slide through the aperture 109 into discharge chute 36 which conveys it to discharge opening 37 where it is held by stops 38 and 39 until removed by the operator.

Referring now to the circuit diagram in FIG. 6, in which all switches are shown in normal condition and all solenoids in 'de-energized condition, when the on-olf master switch is closed, the closure of the normally open start microswitch 61 as a result of a moist matrix hitting the stop 35 completes a circuit to a timer solenoid 91 within the timer 62. The apparatus of the timer 62 is shown schematically Within the dashed line in FIG. 6. The energization of the timer solenoid 91 closes the timer contact switches 92 and 94. The closing of the timer switch 92 causes the timer motor 95 to commence running through the circuit thereby completed. And the closing of the timer switch 94 completes a circuit to a start solenoid 96 which in its energized condition maintains the normally open switches 97, 98, 99 and 100 in closed condition. The closing of the switches 97, 98 and 99 turns on the infra-red heating lamps 22 and 23 and also the motors 101 and 108 of the exhaust blowers 3t) and 106. The closing of the switch 10-!) completes a holding circuit around the start microswitch 61 so that the timer continues to operate even though the start microswitch 61 is opened, as might occur from shrinkage of the moist matrix away from the stop 35 during the pre-drying period. When the timer 62 has run for the pre-set time period, the timer motor 95, through a cam action operatively connecting the timer motor and the timer switches, momentarily closes the timer switch 93 and then opens all three switches 92, 93 and 94. The momentary closing of the timer switch 93 momentarily energizes the release solenoid 63 which actuates the release mechanism as heretofore explained. The opening of the timer switches 92 and 94 turns off the timer motor 95, the exhaust blower motors 101 and 108, and the heating lamps 22 and 23 and de-energizes the timer solenoid 91. The timer 62 is shown only schematically in FIG. 6, and it is to be understood that it may be of any conventional type so long as it performs the above-described functions. A preferred form of timer may be an HA Series Microfiex Preset Timer marketed by the Eagle Signal Corporation of Moline, Illinois, set for a switch or contact sequence which will acomplish the above-described functions.

The invention is not to be understood as restricted to the details set forth above, since these may be modified within the scope of the appended claims without departing from the spirit of the invention.

We claim:

1. A matrix pre-drier comprising a ground supported frame, a substantially planar prestressed screen mounted on the frame having suflicient planar area to support sub st-anti-ally planar-1y a side of a moist matrix, said screen having a close mesh and low mass to substantially uni formiy support the entire supported side of the matrix and to expose substantially the entire supported side of the matrix for substantially uniform and even application of heat thereto, heating means on the frame on each side of the screen for applying substantially equal amounts of radiant heat energy substantially uniformly to each side of a matrix supported on the screen, a substantially closed chamber surrounding the screen and the heating means, means connected to the chamber on one side of the screen for creating a differential of gas pressure within the chamher on opposite sides of the screen, means connected to the chamber on the other side of the screen for removing gas therefrom, means for operating simultaneously the heating means, the means for creating the differential of gas pressure and the means for removing gas from the chamber, timer means for selectively preselecting the time period during which the means for operating shall operate, and means responsive to the timer means for turning off the means for operating upon expiration of the preselected time period, whereby a moist matrix may be placed on the high pressure side of the screen and held thereon in substantially planar configuration by means of the pressure differential while substantially equal amounts of radiant heat are applied simultaneously and substantially uniformly to each side of the matrix for a predetermined time period and gas is circulated past the matrix.

2. A pre-drier for shrinking a wet matrix in a flat condition, the pre-drier comprising supporting means for the matrix including a rigid frame having an opening and a wire mesh screen s r t ed across the opening and sec red to the frame to form a flat supporting surface for the matrix, said frame supporting the screen at an inclined angle to the horizontal, means applying differential air pressure on opposite sides of the screen when the matrix is placed across the opening for urging the matrix against the screen with a uniform force over the entire surface, the screen being held under tension by the frame to resist deformation by the pressure of the matrix against the screen, the screen having a sufficiently close mesh to prevent deformation of the wet matrix into the open spaces of the screen by the applied force, means for applying radiant heat energy simultaneously to both sides of the matrix uniformly over the broad surfaces of the matrix, releasable stop means positioned along the lower edge of the frame arranged to normally engage the edge of the matrix, and means for simultaneously actuating the stop means and interrupting operation of the differential pressure means to permit the matrix to drop off the screen under the action of gravity.

3. A pre-drier for shrinking a wet matrix in a flat condition, the pre-drier comprising supporting means for the matrix including a rigid frame having an opening and a wire mesh screen stretched across the opening and secured to the frame to form a flat supporting surface for the matrix, means applying a differential air pressure on opposite sides of the screen when the matrix is placed across the opening for urging the matrix against the screen with a uniform force across the entire surface, the screen being held under tension by the frame to resist deformation by the pressure of the matrix against the screen, the screen having a sufiicien-tly close mesh to prevent deformation of the wet martix into the open spaces of the screen by the applied force, means for applying radiant heat energy simultaneously to both sides of the matrix uniformly over the broad surfaces of the matrix, the frame supporting the screen at an incline angle to the horizontal, releasable stop means positioned along the lower edge of the frame arranged to normally engage the edge of the matrix, and means for simultaneously actuating the stop means and interrupting operation of the differential pressure means to permit the matrix to drop off the screen under the action of gravity.

References Cited by the Examiner UNITED STATES PATENTS 2,442,407 6/ 1948 Gibbons 34-4 X 2,492,348 12/ 1949 Baker. 34-145 X 2,542,654 2/1951 Gadden 34-146 X 2,618,073 11/1952 Finzer 34-146 X 2,728,147 12/ 1955 Imshaug 34-146 2,731,733 1/1956 Griner 34-146 X 3,077,674 2/1959 Mueller 34-151 X FOREIGN PATENTS 199,669 3/ 1958 Austria.

63,576 5/ 1945 Denmark.

937,189 3/1948 France.

935,607 11/ 1955 Germany.

227,393 9/ 1943 Switzerland.

FREDERICK L. MATTESON, In, Primary Examiner.

CHARLES C. OCONNELL, BENJAMIN BENDEIT, GILBERT S. MITCHELL, WILLIAM F. ODEA.

Examiners.

S. I. NOVOSAD, N. YUDKOPF, C. R. REMKE,

Assistant Examiners, 

2. A PRE-DRIER FOR SHRINKING A WET MATRIX IN A FLAT CONDITION, THE PRE-DRIER COMPRISING SUPPORTING MEANS FOR THE MATRIX INCLUDING A RIGID FRAME HAVING AN OPENING AND A WIRE MESH SCREEN STRETCHED ACROSS THE OPENING AND SECURED TO THE FRAME TO FORM A FLAT SUPPORTING SURFACE FOR THE MATRIX, SAID FRAME SUPPORTING THE SCREEN AT AN INCLINED ANGLE TO THE HORIZONTAL, MEANS APPLYING DIFFERENTIAL AIR PRESSURE ON OPPOSITE SIDES OF THE SCREEN WHEN THE MATRIX IS PLACED ACROSS THE OPENING FOR URGING THE MATRIX AGAINST THE SCREEN WITH A UNIFORM FORCE OVER THE ENTIRE SURFACE, THE SCREEN BEING HELD UNDER TENSION BY THE FRAME TO RESIST DEFORMATION BY THE PRESSURE OF THE MATRIX AGAINST THE SCREEN, THE SCREEN HAVING A SUFFICIENTLY CLOSE MESH TO PREVENT DEFORMATION OF THE WET MATRIX INTO THE OPEN SPACES OF THE SCREEN BY THE APPLIED FORCE, MEANS FOR APPLYING RADIANT HEAT ENERGY SIMULTANEOUSLY TO BOTH SIDES OF THE MATRIX UNIFORMLY OVER THE BROAD SURFACES OF THE MATRIX, RELEASABLE STOP MEANS POSITIONED ALONG THE LOWER EDGE OF THE FRAME ARRANGED TO NORMALLY ENGAGE THE EDGE OF THE MATRIX, AND MEANS FOR SIMULTANEOUSLY ACTUATING THE STOP MEANS AND INTERRUPTING OPERATION OF THE DIFFERENTIAL PRESSURE MEANS TO PERMIT THE MATRIX TO DROP OFF THE SCREEN UNDER THE ACTION OF GRAVITY. 